Multidimensional Functionally Graded Materials (ε/σ-MFGM) for HVDC GIL/GIS Spacers

This study discusses the multidimensional functionally graded materials (MFGMs) for spacers in high voltage direct current gas-insulated transmission lines and switchgears (HVDC GILs/GISs). The effects of surface conductance graded materials ( $\sigma $ -SFGMs) and bulk permittivity graded materials ( $\varepsilon $ -FGMs) on the electric field distributions along the basin-type spacer are investigated under dc stationary and transient conditions. Results show that the $\sigma $ -SFGM spacer can effectively regulate the steady-state electric field, but the regulation effect on the transient electric field is limited when its time constant is longer than the transient time of the applied voltage. The $\varepsilon / \sigma $ -MFGM spacer with both bulk permittivity and surface conductance gradients has the same relaxation effect on the stationary electric field as the $\sigma $ -SFGM spacer and the same effect on the transient electric field as the $\varepsilon $ -FGM spacer, which can coordinately regulate the electric field distribution under multiple operating conditions in HVDC GIL/GIS. Compared to the uniform spacer, the $\varepsilon / \sigma $ -MFGM spacer can reduce the maximum electric field strengths under steady state, switching-on, and dc-impulse conditions by 38.9%, 18.6%, and 28.2%, respectively.